The invention relates to a color display device comprising an in-line electron gun for generating three electron beams, a phosphor screen on an inner surface of a display window, and a unit for deflecting the electron beams across the color selection electrode.
Such display devices are known.
A current aim is to make the outer surface of the display window flatter, so that the image represented by the color display device is perceived by a viewer as flat. However, an increase of the radius of curvature of the outer surface will lead to an increase of a number of problems. The radius of curvature of the inner surface of the display window and the color selection electrode should increase, and, as the color selection electrode becomes flatter, the strength of the color selection electrode decreases and hence the sensitivity to doming and vibrations increases. An alternative solution to this problem would be to curve the inner surface of the display window more strongly than the outer surface. By virtue thereof, a color selection electrode having a relatively small radius of curvature can be used. As a result, doming and vibration problems are reduced, but other problems occur instead. The thickness of the display window is much smaller in the center than at the edges. As a result, the weight of the display window increases and the intensity of the image decreases substantially towards the edges.
EP 0,421,523 discloses a color cathode ray tube with an in-line gun, a pin cushion correcting yoke and an eyebrow effect electronoptical distortion correction device comprising two pairs of coils, each pair having a coil on each outer electron beam side of the neck in the plane of the beams. The coil pairs are spaced apart along the z-axis between the gun and the yoke and are driven by a sawtooth current having a bow-tie envelope synchronous with the raster scan to correct the dynamic, asymmetrical eyebrow effect which is apparent as a purity defect on the raster.
WO 99/34392 describes a color display device comprising a color cathode ray tube including an in-line electron gun for generating three electron beams located substantially within a plane extending in an X-direction of a rectangular X-Y coordinate system, a color selection electrode, deflection means for deflecting the electron beams located at a deflection plane, and first and second influencing means to dynamically influence the convergence of the electron beams, to decrease a distance between the electron beams at a location of the deflection plane.
In the non-prepublished applications U.S. Ser. No. 09/338048 and U.S. Ser. No. 09/338049 advantageous embodiments of the first and second deflection means are described.
It is an object of the invention to provide an improved color display device. To this end, the invention provides a color display device as defined in the independent claim. The dependent claims define advantageous embodiments.
These and other objects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.